Fair Value Measurements (Summary Of Asset Impairment And Decommission Costs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Asset impairment	$ 19,217	$ 10,287	$ 3,042
Gain on sale of fiber assets	(8,919)
Other disposal costs	83
Total asset impairment and decommission costs	30,242	94,783	23,801
Former Corporate Headquarters Building [Member]
Write-offs relating to long-lived assets and intangibles	2,345	1,154
Not Identified by Segment [Member]
Write-offs relating to long-lived assets and intangibles	4,549	5,378	5,417
Total asset impairment and decommission costs	2,345
Fiber Assets [Member]
Write-offs relating to long-lived assets and intangibles		56,733
Decommissioned Towers [Member]
Write-offs relating to long-lived assets and intangibles	$ 12,967	$ 21,231	$ 15,342